1. Field of the Invention
The present invention concerns electromechanical positioning systems, and more particularly an electromechanical positioning system for a mirror in a head up display.
2. Description of Related Art
A head-up display or HUD is a transparent display panel that presents information to a user without requiring him to look away from a preferred viewing direction. For example, a driver can view traffic and the road in front of the vehicle through the transparent panel of the HUD. A typical HUD includes a combiner, a projector, and a video data source such as a computer. The combiner is the transparent panel that is located in front of the person observing the display. The combiner usually includes one or more optical coatings that reflect only those specific wavelengths of monochromatic light that are projected by the HUD projector. The combiner can be thought of as a semi-transparent mirror. The HUD projector is usually mounted above or below the combiner. Images containing graphics or data are projected by the projector toward the combiner, which then projects the images toward the user.
Combiner positioning mechanisms for a HUD, which can move the combiner between a storage position and an operating position, are known in the art. For example, one such combiner is disclosed in PCT Publication No. WO 2007/057608 A1. Such positioning mechanisms have stored the combiner in a protected chassis when in a storage position. The combiner is mounted on a movable support that is displaceable between a rest position and a display position. The blade is retracted when the movable support is in the rest position and the combiner is extended from the chassis when the movable support is in the display position.
Still, combiner positioning mechanisms require careful consideration to ensure the performance in all kinds of environmental conditions such as high humidity, extreme temperatures, and the presence of contaminants that can cause corrosion. In such systems, careful choice of materials and design are necessary to provide smooth motion.
Repeatable positional accuracy is also important for combiner positioning mechanisms because an improperly positioned combiner will not function properly in a HUD system. Such positional accuracy can be achieved using high precision parts that are manufactured and maintained to very close tolerances. However, the need for such close tolerances has the undesirable effect of increasing the manufacture and maintenance expense associated with the positioning mechanism.
Another key design consideration relates to vibration. A mobile HUD system must have a high resistance to vibration in order to provide a stable image for the user. Failure to control vibration associated with the combiner in particular can result in a display that is irritating for the viewer and unpleasant to use over extended periods. Accordingly, a positioning system for a combiner in a HUD should have a high stability and a high natural frequency.